Search results for "autoregulation"

Dynamic cerebrovascular autoregulation in patients prone to postural syncope: Comparison of techniques assessing the autoregulation index from sponta…

2021

Abstract Three approaches to the assessment of cerebrovascular autoregulation (CA) via the computation of the autoregulation index (ARI) from spontaneous variability of mean arterial pressure (MAP) and mean cerebral blood flow velocity (MCBFV) were applied: 1) a time domain method (TDM); 2) a nonparametric method (nonPM); 3) a parametric method (PM). Performances were tested over matched and surrogate unmatched pairs. Data were analyzed at supine resting (REST) and during the early phase of 60° head-up tilt (TILT) in 13 subjects with previous history of postural syncope (SYNC, age: 28 ± 9 yrs.; 5 males) and 13 control individuals (noSYNC, age: 27 ± 8 yrs.; 5 males). Analysis was completed b…

Profil des interactions maitre-élèves: perceptions divergentes dans la classe

2008

The Effect of Dexamethasone on Water and Electrolyte Content and on rCBF in Perifocal Brain Edema in Man

1972

The results of clinical studies are reported dealing with the relationship between cerebral edema and regional cerebral blood flow in patients with brain tumor as well as with the effect of dexamethasone on this relationship. rCBF is found to be significantly reduced in brain tissue surrounding brain tumors. Autoregulation as well as cerebrovascular reactivity to PaCO2 is focally or generally impaired. Water content of perifocal white matter is markedly increased. The combination of tissue lactacidosis, low regional blood flow and vasoparalysis seems to be a characteristic finding in this type of local brain edema. The increased local tissue pressure, due to the increased tissue water conte…

Spectral decomposition of cerebrovascular and cardiovascular interactions in patients prone to postural syncope and healthy controls.

2022

We present a framework for the linear parametric analysis of pairwise interactions in bivariate time series in the time and frequency domains, which allows the evaluation of total, causal and instantaneous interactions and connects time- and frequency-domain measures. The framework is applied to physiological time series to investigate the cerebrovascular regulation from the variability of mean cerebral blood flow velocity (CBFV) and mean arterial pressure (MAP), and the cardiovascular regulation from the variability of heart period (HP) and systolic arterial pressure (SAP). We analyze time series acquired at rest and during the early and late phase of head-up tilt in subjects developing or…

Nonlinear effects of respiration on the crosstalk between cardiovascular and cerebrovascular control systems.

2016

Cardiovascular and cerebrovascular regulatory systems are vital control mechanisms responsible for guaranteeing homeostasis and are affected by respiration. This work proposes the investigation of cardiovascular and cerebrovascular control systems and the nonlinear influences of respiration on both regulations through joint symbolic analysis (JSA), conditioned or unconditioned on respiration. Interactions between cardiovascular and cerebrovascular regulatory systems were evaluated as well by performing correlation analysis between JSA indexes describing the two control systems. Heart period, systolic and mean arterial pressure, mean cerebral blood flow velocity and respiration were acquired…

Sevoflurane Impairs Cerebral Blood Flow Autoregulation in Rats: Reversal by Nonselective Nitric Oxide Synthase Inhibition

2005

UNLABELLED In this study, we investigated the effects of 1.0 and 2.0 minimum alveolar anesthetic concentration (MAC) sevoflurane on cerebral blood flow (CBF) autoregulation before and after nonselective inhibition of nitric oxide (NO) synthase in rats. Rats were randomly assigned as follows: Group 1 (n = 8): 1.0 MAC sevoflurane; Groups 2 and 3 (n = 8 per group): 2.0 MAC sevoflurane. Assessment of autoregulation within a mean arterial blood pressure range of 140-60 mm Hg was performed by graded hemorrhage before and after administration of l-arginine methyl ester (l-NAME, 30 mg/kg IV, Groups 1 and 2) or during hypocapnia (Group 3). In 10 additional animals, brain tissue NO(2)(-) concentratio…

Cerebral Blood Flow Regulation Under the Conditions of Arterial Hypoxia

1978

Pronounced arterial hypoxia induces a decrease of cerebrovascular resistance and an increase of total and regional cerebral blood flow. Under the conditions of normal arterial blood pressure and normal acid base status, the changes of both parameters commence when the oxygen tension in the arterial blood decreases below approximately 50 mm Hg. At the same time, the oxygen tension in the cerebral venous blood reaches values below approximately 28 mm Hg. Different authors [23, 28, 30, 31, 33] reported that cerebral blood flow responses to PaO2 decrease are threshold at these oxygen tensions. The threshold oxygen tension of cerebral venous blood was accorded a special significance because Noel…

Usefulness of Cerebral Oximetry in TBI by NIRS

2021

Measurement of cerebral oximetry by near-infrared spectroscopy provides continuous and non-invasive information about the oxygen saturation of haemoglobin in the central nervous system. This is especially important in the case of patients with traumatic brain injuries. Monitoring of cerebral oximetry in these patients could allow for the diagnosis of inadequate cerebral oxygenation caused by disturbances in cerebral blood flow. It could enable identification of episodes of hypoxia and cerebral ischemia. Continuous bedside measurement could facilitate the rapid diagnosis of intracranial bleeding or cerebrovascular autoregulation disorders and accelerate the implementation of treatment. Howev…

Exploring metrics for the characterization of the cerebral autoregulation during head-up tilt and propofol general anesthesia

2022

Techniques grounded on the simultaneous utilization of Tiecks' second order differential equations and spontaneous variability of mean arterial pressure (MAP) and mean cerebral blood flow velocity (MCBFV), recorded from middle cerebral arteries through a transcranial Doppler device, provide a characterization of cerebral autoregulation (CA) via the autoregulation index (ARI). These methods exploit two metrics for comparing the measured MCBFV series with the version predicted by Tiecks' model: normalized mean square prediction error (NMSPE) and normalized correlation rho. The aim of this study is to assess the two metrics for ARI computation in 13 healthy subjects (age: 27 & PLUSMN; 8 yr…

Effects of physical provocations on heart rate reactivity and reactive aggression in children

2006

This article presents complementary data on the relationship between the intensity of offensive and defensive aggression that was investigated by means of the computerised Pulkkinen Aggression Machine (PAM) paradigm [Juujarvi et al., 2001; Aggr Behav 27:430-445]. The recording of the electrocardiogram was conducted in a sample of 109 children (61 boys and 48 girls) while they completed the PAM. Across the conditions of controlled aggression, the simulated attack and defence evoked a mean increase of HR by 2.7 beats per minute (bpm), but the variation between children was substantial (-10.9 to +11.4 bpm). Children who showed a strong HR increase, moderate HR increase, or HR decrease were com…